Method for continuous graphitization of carbonaceous thread



April 11, 1967 Q CR ET AL 3,313,597

METHOD FOR CONTINUOUS GRAPHITIZATION OF CARBONACEOUS THREAD Filed Jan. 24, 1963 INVENTORS GEORGE E.CRANCH JULIUS S. SHINKO 3,313,597 Patented Apr. 11, 1967 3,313,597 METHOD FOR CONTINUOUS GRAPHITIZATION OF CARBONACEOUS THREAD George E. Cranch and Julius S. Shinko, Fostoria, Ohio, assignors to Union Carbide Corporation, a corporation of New York Filed Jan. 24, 1963, Ser. No. 253,593 8 Claims. (Cl. 23209.3)

The invention relates to a method and an apparatus for graphitizing a carbonaceous thread.

A process was recently developed for converting cellulosic textile material into a graphitic material which has the chemical and electrical attributes of natural graphite while substantially retaining the physical textile properties of the original cellulosic material. It was found that cloths, felts, braids, yarns, knits, monofilaments, weaves, and the like can be so graphitized by subjecting them to a carefully controlled heating schedule in a furnace. The heating schedule broadly comprises a first heating stage up to about 900 C. in which the rate of temperature increase is below about 100 C. per hour and a second heating stage up to graphitization temperature (between about 1300 C. and about 3000 C.) in which the rate of temperature increase may be up to about 3000 C. per hour and higher.

Since the process outlines above is inherently a batch process, a large amount of energy is required for each batch to heat both the cellulosic material and the furnace from about room temperature to a temperature of up to about 3000 C. Furthermore, a process which is capable of operating continuously is almost always preferred for commercial operations.

There are also several processes known in the art for carbonizing a textile material, such as the processes described in United States Patent 3,053,775, which issued to W. F. Abbott on Sept. 11, 1962, and United States Patent 3,011,951, which issued to W. T. Soltes on Dec. 5, 1961. Since graphite thread is better than carbon thread for many purposes, a process which can convert carbonized thread to graphite thread is desirable.

The main object of the invention, therefore, is to provide both a process and an apparatus for graphitizing a carbonaceous thread, which process and apparatus are capable of substantially continuous operation.

Another object is to provide an improvement in a process for graphitizing carbonaceous thread to form a flexible, electrically conductive graphite thread.

The single figure in the drawing is a fragmentary perspective view of an apparatus in accordance with the invention for continuously graphitizing a moving carbonaceous thread.

Broadly, the invention comprises a process in which a carbonaceous thread comp-rising at least about 90 percent by Weight carbon is passed over a pair of spaced electrical contacts in the direction of its length and an electric current is supplied to the contacts in an amount sufiicient to raise the temperature of the thread between the contacts as it passes over the contacts to graphitization temperature.

The apparatus of the invention comprises a pair of spaced, electrically conductive rollers over which a thread may pass, means for supplying electric current to the rollers in an amount sufiicient to raise the temperature of the thread between the rollers as it passes thereover to graphitization temperature, and means for controlling the atmosphere around the thread completely between the rollers.

Referring now to the drawing, the apparatus there shown for continuously graphitizing a moving carbonaceous thread 10 comprises a pair of rollers 11 and 12 held in spaced relationship by suitable supports (not shown). A means for supplying electrical energy to the rollers 11 and 12 is associated with the rollers 11 and 12, and may comprise the spring-mounted electrical contacts 14 and 16, or a brush or other electrical contact arrangement with the rollers 11 and 12, along with a suitable source of electricity (not shown). A means for removing condensate from the rollers 11 and 12 is preferably provided, and comprises a heat source 18 directed at the rollers and a pair of scrapers 20 and 22 disposed against the peripheral surfaces of the rollers 11 and 12. The condensate results from the volatiles in the incoming thread 10 condensing on the relatively cool rollers 11 and 12.

A gas trough 24 including a plurality of gas inlets 26 is provided between the rollers 11 and 12 to control the atmosphere around the moving thread 10 completely between the rollers 11 and 12, Le, along the thread from electrical contact with the roller 11 to electrical contact with the roller 12. Control of the atmosphere may also be accomplished by a chamber or other means, but a gas trough has been found to be the most convenient. An oxygen-free atmosphere is preferably provided around the thread 10 to avoid oxidation of the carbonaceous thread, unless of course an oxidized product is desirable. Nitrogen and other gases inert to carbon and graphite such as argon, neon, helium, other rare gases, hydrogen, carbon monoxide, ammonia, and mixtures thereof are preferred.

The incoming carbonaceous thread 10 is graphitized between the rollers 11 and 12 by the heat generated within itself as a result of the electric current flowing through it. The voltage required to graphitize the thread will vary depending on the resistance of the thread between the rollers (which of course depends on the resistivity of the thread and the spacing between the rollers) and the rate at which the thread passes over the rollers, but the voltage may be represented generically as that voltage necessary to attain a temperature in the thread of at least about 1300 C. near the output roller, i.e., a temperature suflicient to graphitize the thread. Operating temperatures of between about 1800 C. and 3000 C. are preferred.

The rollers 11 and 12 may be made of any electrically conductive material which is durable at the graphitization temperature employed, preferably at temperatures up to 3000 C., such as graphite, refractory materials in gen eral, suitably cooled metals, and the like, and a phos phorous bronze alloy or other conductive material is suitable for the electrical contacts 14 and 16. The scrapers 20 and 22 and the heat source 18 can be of a conventional design, and are suitably made of a conventional material, such as a bronze alloy. Graphite is the preferred material for the rollers 11 and 12.

The incoming carbonaceous thread 10 must consist of at least about percent by weight carbon, the remainder consisting essentially of materials which are volatile at graphitization temperatures, to obtain a good, flexible graphite product. If the incoming carbonaceous thread 10 contains above about 10 percent by weight volatile materials, it tends to rupture and break during graphitization. A thread containing at least about 90 percent carbon can be obtained by slowly heating in a furnace a cellulosic material, such as rayon or other regenerated cellulosic materials, or other materials which carbonize without undue ruptures and volatilization, such as polyacrylonitrile. Rayon is the preferred material. Such carbonization procedures are known in the art as mentioned hereinbefore.

In general, the cellulosic or other material must be heated to a temperature between about 700 C. and 1100 C. to effect a 90 percent by weight carbonization, and the rate of temperature increase must be below about C. per hour. Preferably, a rate of temperature increase of up to about 55 C. per hour is employed up to a temperature of about 400 C. followed by a rate of increase of up to about 100 C. per hour until a temperature is reached at which at least about 90 percent carbonization is obtained. The process of the invention for graphitization is not limited by a rate of temperature increase, and indeed the graphitization takes place very rapidly.

Another reason for the requirement of a starting material containing at least about 90 percent carbon in the process of the invention is that at lower carbon contents arcing between the moving thread and the electrical contacts, e.g., rollers 11 and 12, is so severe that the physical condition of the thread is impaired. This effect is not present in batch-type electrical heating processes, but it is an important consideration in processes considered as continuous. It has been found that in general a carbonaceous thread containing at least about 90 percent carbon will have an electrical resistivity no greater than about four times that of the graphitized final product.

The graphite thread produced by the process of the invention is a flexible, electrically conductive, relatively strong material which can be creased or folded many times without damage. For example, 1650/ 720/ 10 denier unprocessed rayon yarn was carbonized in a furnace under a slow heating schedule as outlined herein with a final temperature of about 900 C. The electrical resistance of the carbonized yarn was about 8 ohms per inch. This yarn was then passed over two spaced graphite rollers with an impressed voltage of about 80 volts The rollers were so spaced and the rate at which the yarn moved was so adjusted that approximately 8 amperes flowed through the yarn and the final yarn temperature was about 3000 C. The graphite yarn product was flexible and possessed an average strength of 17 to 19 pounds and an average resistance of about 2.5 to 3.0 ohms per inch. The energy consumption for the graphitization step was 0.8 kilowatt-hour. Graphite yarn produced in a tube furnace possessed similar properties but required about 300 kilowatt-hours for the same amount of yarn.

The threads in woven materials, such as tapes, can be graphitized in accordance with the invention by providing an apparatus of a suitable size. The fibers perpendicular to current flow will be graphitized by the heat generated in the other fibers. Threads can also be graphitized by passing them through or over spaced electrical contacts other than rollers, such as two spaced, electrically energized bodies of an ionized gas or mercury.

The present process and apparatus can also be modified to provide a stronger graphite yarn by stretching the yarn as it becomes plastic, usually at about 2200" C. For example, an output roller running at slightly higher speed than the input roller will strengthen the yarn in this manner. Similarly, yarn shrinkage can be achieved by running the output roller at a slower speed than the input roller.

It will be appreciated by those in the art that the process and apparatus of the invention permits easy and Cit ill

rapid control of process temperatures, atmospheres, and through-put rates. Furthermore, the energy required to graphitize a given quantity of yarn is far less than that required in accordance with the procedures of prior art.

What is claimed is:

1. A process for continuously graphitizing a carbonaceous thread comprising at least about 90 percent by weight carbon, which process comprises providing a pair of spaced electrical contacts, passing said thread in the direction of its length across said pair of contacts, and supplying an electric current through said contacts and through said thread in an amount suflicient to raise the temperature of said thread between said contacts as said thread passes over said contacts to graphitization temperature.

2. The process defined in claim 1 wherein said graphitization temperature is between about 1800 C. and about 3000 C.

3. A process for continuously graphitizing a carbona' ceons thread comprising at least about 90 percent by weight carbon, which process comprises providing a pair of spaced electrical contacts, passing said thread in the direction of its length across said pair of contacts, maintaining a controlled atmosphere around said thread between said contacts and supplying an electric current through said contacts and through said thread in an amount sufficient to raise the temperature of said thread between said contacts as said thread passes over said contacts to graphitization temperature.

4. The process defined in claim 3 wherein said atmosphere is free of oxygen.

5. The process defined in claim 3 wherein said graphitization temperature is between about 1800 C. and about 3000 C.

6. A process for continuously graphitizing a carbonaceous thread comprising at least about 90 percent by weight carbon, which process comprises providing a pair of spaced, electrically conductive rollers, passing said thread in the direction of its length over said pair of rollers, maintaining a controlled atmosphere around said thread between said rollers, and supplying an electric current through said rollers and through said thread in an amount sufficient to raise the temperature of said thread between said rollers as said thread passes over said rollers to graphitization temperatures.

7. The process defined in claim 6 wherein said atmosphere is free of oxygen.

8. The process defined in claim 6 wherein said graphitization temperature is between about 1800 C. and about 3000 C.

References Cited by the Examiner UNITED STATES PATENTS 1,704,036 3/1929 Cope l48154 X 3,011,981 12/1961 Soltes 252502 3,107,152 10/1963 Ford et al. 23209.2 3,116,975 '7/1964 Cross et al. 23-209.4

OSCAR R. VERTIZ, Primary Examiner.

E. J. MEROS, Assistant Examiner.

UNITED STATES PATENT OFFICE Certificate Patent No. 3,313,597 Patented Apr. 11, 1967 George E. Cranch and Julius S. Shinko Application having been made by George E. Cranch and Julius S. Shinko, the inventors named in the patent above identified; and Union Carbide Corporation, New York, New York, a corporation of New York, the assignee, and Willie H. Watts of Perma, Ohio, for the issuance of a. certificate under the provisions of Title 35, Section 256, of the United States Code, adding the name of the said Willie H. Watts as a joint inventor, and a showing and proof of facts satisfying the requirements of the said section having been submitted, it is this 24th day of December 1968, certified that the name of the said Willie H. Watts is hereby added to the said patent as a joint inventor with the said George E. Cranch and Julius S. Shinko.

EDWIN L. REYNOLDS,

First Assistant Commissioner 0 f Patents.

[SEAL] 

1. A PROCESS FOR CONTINUOUSLY GRAPHITIZING A CARBONACEOUS THREAD COMPRISING AT LEAST ABOUT 90 PERCENT BY WEIGHT CARBON, WHICH PROCESS COMPRISES PROVIDING A PAIR OF SPACED ELECTRICAL CONTACTS, PASSING SAID THREAD IN THE DIRECTION OF ITS LENGTH ACROSS SAID PAIR OF CONTACTS, AND SUPPLYING AN ELECTRIC CURRENT THROUGH SAID CONTACTS AND THROUGH SAID THREAD IN AN AMOUNT SUFFICIENT TO RAISE THE TEMPERATURE OF SAID THREAD BETWEEN SAID CONTACTS AS SAID THREAD PASSED OVER SAID CONTACTS TO GRAPHITIZATION TEMPERATURE. 